The present invention relates to methods of producing articles having alternating magnetic and non-magnetic portions from continuous metal blanks.
Such articles are widely used as machine and instrument components. These articles are usually manufactured (joined together) from metals featuring different (contrasting) properties, such as, magnetic and non-magnetic properties high and low electric resistance, different coefficients of thermal expansion, different Curie points and different strength and plasticity characteristics. The metals featuring the above-specified properties are typically either bonded by welding, soldering, cementing together, pouring, cladding or by making use of mechanical connections, such as, riveting. They can be also joined together by hot or cold pressure shaping.
However, when metal articles are produced by the above-described methods, they suffer from deterioration of the properties of the metals which contribute to the formation of the magnetic and non-magnetic portions. Moreover, the fabrication of the articles composed of separate parts is associated with a number of technological problems. Thus, metals having different crystalline structures, such as, steels belonging to an austenitic (non-magnetic) and martensitic (magnetic) class can be bonded together by welding. In order to prevent hot cracking, austenitic steels are welded with a low arc heat input and a maximum possible cooling rate. Martensitic steels, to prevent cold cracking they are welded with high arc heat inputs and with an accompanying tempering or preheating steps to prevent the formation of cold cracks. However, when welding magnetic and non-magnetic metals, the use of the above-specified techniques adversely affects the properties of one of the metals being connected, and results in a reduction in strength, plasticity and impact toughness. In addition, the metals joined together by welding are subjected to temperatures approaching their melting points thus ensuing the alteration of their initial structures and with the magnetic properties of the article being uncontrollable in the welding zone. Local mixing of the metal is also conducive to uncontrollable properties at the metal weld. As a rule, a weld joint is inferior in strength to the base metal. For certain constructions welding is not applicable and the welding of heterogeneous metals presents certain problems or is not feasible.
Joining metals together by a combined hot and cold pressure treatment or by pouring one metal into another enables the production of a strong article. However, such a monolithic article consists of metals differing in their crystalline structures, such as, one metal having an austenitic non-magnetic structure and another metal having a martensitic magnetic structure. Heat treatment of a bimetallic blank results in a sharp deterioration of the magnetic and mechanical characteristics of one of the metals from which the articles has been fabricated so that it is difficult and sometimes impossible to improve the properties of the magnetic and non-magnetic portions with the aid of heat treatment.
Mechanical connecting and cementing of magnetic and non-magnetic metals cannot ensure high reliability, stress-rupture properties and serviceability of the articles thus produced.
The inventors have disclosed in application Ser. No. 515,663 filed Oct. 17, 1974 now U.S. Pat. No. 3,953,252 a method of producing metal articles having magnetic and non-magnetic portions, comprising heat treating separate portions of a continuous metal blank manufactured from a metal of a specified chemical composition to a temperature ranging from 450.degree. to 1000.degree. C. and heating the other portions to a temperature exceeding 1000.degree. C to the melting point of the blank with the integrity of the blank being undisturbed.
The results of the above method were superior to those attainable heretofore.
It is common knowledge that certain alloys upon being subjected to an appropriate heat treating operation acquire or lose their magnetic properties. An alloy containing, in percent by weight: 12-14 vanadium and 50-52 cobalt and featuring low magnetic properties, and upon being subjected to cold working, acquires the properties of a magnetically hard material. (E. Gudreman "Special Steels", USSR, Metallurgia Publishers, 1966, Vol. 2, p.967).
The inventors have taken into account these phenomena in their containing research aimed at selecting the proper material for the blanks and the proper combination of heat treatment and deformation. In addition, blanks of different configuration have been studied and subjected to different kinds of deformation.
The known methods do not allow for the changing of the configuration of the magnetic and non-magnetic portions by local heat treatment.
Components having magnetic and non-magnetic portions find application in electronic computers. However, the components manufactured by cementing together magnetic and non-magnetic materials have inadequate life periods.
In cybernetics use is made of parts having magnetic and non-magnetic portions, the parts being fabricated by depositing magnetic powders on a non-magnetic substratum (a matrix, strip or backing, e.g. in plastics). To this end the matrix portions which are to remain non-magnetic are covered with an impervious film, whereas those portions which are to become magnetic remain exposed. However, the deposited magnetic layer does not have the requisite longevity.
The lack of procedure which would enable the production of strong metal articles having magnetic and non-magnetic portions creates difficulties in a number of industries.